1. Field of the Invention
This invention relates to a method of manufacturing an electron-emitting device, a method of manufacturing an electron source and a method of manufacturing an image-forming apparatus comprising such an electron source.
2. Related Background Art
There have been known two types of electron-emitting device; the thermoelectron emission type and the cold cathode electron emission type. Of these, the cold cathode emission type refers to devices including field emission type (hereinafter referred to as the FE type) devices, metal/insulation layer/metal type (hereinafter referred to as the MIM type) electron-emitting devices and surface conduction electron-emitting devices.
Examples of FE type device include those proposed by W. P. Dyke and W. W. Dolan, xe2x80x9cField emissionxe2x80x9d, Advances in Electron Physics, 8, 89 (1956) and C. A. Spindt, xe2x80x9cPhysical Properties of thin-film field emission cathodes with molybdenum conesxe2x80x9d, J. Appl. Phys., 47, 5248 (1976).
Examples of MIM device are disclosed in papers including C. A. Mead, xe2x80x9cOperation of Tunnel-Emission Devicesxe2x80x9d, J. Appl. Phys., 32, 646 (1961).
Examples of surface conduction electron-emitting device include one proposed by M. I. Elinson, Radio Eng. Electron Phys., 10 (1965).
Known image-forming apparatus utilizing cold cathode type electron-emitting devices include flat type electron beam display panels realized by arranging an electron source substrate carrying thereon a large number of electron-emitting devices and an anode substrate provided with a transparent electrode and a fluorescent body vis-a-vis and in parallel with each other within an envelope and evacuating the envelope.
I. Brodie, xe2x80x9cAdvanced technology: flat cold-cathode CRT""sxe2x80x9d, Information Display, 1/89, 17 (1989) describes an image-forming apparatus comprising field emission type electron-emitting devices.
On the other hand, Japanese Patent Application Laid-Open No. 7-235255 discloses an image-forming apparatus comprising surface conduction electron-emitting devices.
When compared with currently popular cathode ray tubes (CRTs), flat type electron beam display panels are more adapted for light weight and large screen image-forming apparatus. They can provide bright and high quality images than other known flat type display panels including those utilizing liquid crystal, plasma display panels and electroluminescent display panels.
Now, a known surface conduction electron-emitting device and a method of manufacturing such a device as well as a display panel comprising such devices and a method of manufacturing the same as disclosed in the above cited Japanese Patent Application Laid-Open No. 7-235255 will be briefly summarized below.
FIG. 18 of the accompanying drawings schematically illustrates a surface conduction electron-emitting device of the type under consideration. Referring to FIG. 18, it comprises a substrate 1, a pair of device electrodes 2 and 3 and an electroconductive thin film 4, which thin film is typically a palladium thin film formed by baking a film of an organic palladium compound. An electron-emitting region 5 will be produced therein when subjected to a current conduction process referred to as energization forming, which will be described hereinafter.
Conventionally, the electroconductive thin film 4 of a surface conduction electron-emitting device is subjected to energization forming in order to produce an electron-emitting region 5 before the device is put to use for electron emission. In an energization forming process, a constant DC voltage or a slowly rising DC voltage that rises very slowly typically at a rate of 1V/min. is applied to given opposite ends of the electroconductive film 4 to partly destroy, deform or transform the film and produce an electron-emitting region 5 which is electrically highly resistive. Thus, the electron-emitting region 5 is part of the electroconductive film 4 that typically contains a fissure or fissures therein so that electrons may be emitted from the area including the fissure(s) and its vicinity. Note that, once subjected to an energization forming process, a surface conduction electron-emitting device comes to emit electrons from its electron emitting region 5 whenever an appropriate voltage is applied to the electroconductive film 4 to make an electric current run through the device.
After the energization forming process, the device is preferably subjected to an activation process, which is a process for remarkably changing the device current If and the emission current Ie of the device.
An activation process is typically conducted by repetitively applying an appropriate pulse voltage to the electron-emitting region in an atmosphere containing gaseous organic substances. As a result of this process, carbon or a carbon compound arising from the organic substances contained in the atmosphere is deposited on the device to remarkably change the device current If and the emission current Ie.
On the other hand, a display panel to be used for an image-forming apparatus can be prepared by placing an electron source substrate carrying thereon a large number of electron-emitting devices that are arranged in the form of a matrix or parallel ladders and a face plate provided with a fluorescent body adapted to emit light when irradiated with electrons emitted from the electron source substrate and, if necessary, a control electrode vis-a-vis and in parallel with each other within a vacuum envelope.
FIG. 19 of the accompanying drawings schematically illustrates a display panel comprising an electron source realized by arranging surface conduction electron-emitting devices in the form of a matrix. In FIG. 19, the electron source comprises an electron source substrate 201 carrying thereon a plurality of electron-emitting devices, a rear plate 202 rigidly holding the electron source substrate 201 and a face plate 203 realized by arranging a fluorescent film 204 and a metal back 205 on the inner surface of a glass substrate. Reference numeral 206 denotes a support frame to which the rear plate 202 and the face plate 203 are bonded by means of frit glass. Reference numeral 207 denotes a vacuum envelope provided with terminals Dox1 through Doxm and Doy1 through Doyn arranged in correspondence to the matrix of wires in the electron source and a high voltage terminal 208.
A display panel as described above can be made to emit electrons from selected electron emmitting devices arranged on the electron source substrate in a simple matrix arrangement by selectively applying a drive pulse voltage to them. A DC voltage as high as 1 to 10 kV is applied to the high voltage terminal 208 in order to satisfactorily energize the fluorescent body relative to the electron beams emitted from the devices.
An image-forming apparatus capable of displaying highly bright images with high quality can be realized by combining a display panel comprising surface conduction electron-emitting devices and an appropriate drive circuit in a manner as described above.
As discussed above, with any typical known method of manufacturing a surface conduction electron-emitting device, an electron-emitting region 5 is normally produced by subjecting the electroconductive thin film 4 to an energization forming process. This process consumes a considerable amount of electricity for electrically energizing the electroconductive thin film. When preparing a large number of surface conduction electron-emitting devices on a common substrate, it is preferable that a relatively large number of them are subjected to energization forming simultaneously in a single operation (for example, on a row by row basis) but the number may inevitably be limited if each device consumes a considerable amount of electricity for energization forming. This problem has so far been avoided by reducing the thickness of the electroconductive thin film 4 and/or by using a film comprising fine particles for the electroconductive thin film 4 in order to reduce the power consumption rate.
In other words, an ultrathin film or a fine particle film to be used as the electroconductive thin film of a surface conduction electron-emitting device has an advantage that it consumes little power for energization forming because it is fused and aggregated at temperatures lower than the melting point of a bulk of the material of the electroconductive film.
On the other hand, the process of manufacturing a display panel comprising surface conduction electron-emitting devices involves a heating step as described below after the formation of an electroconductive thin film in each device.
Firstly, the envelope 207 of the display panel is a container comprising a rear plate 202, a face plate 203 and a support frame 206 that has to be exhausted in order to produce a vacuum condition in the inside. Thus, these components are typically bonded together by means of frit glass but this bonding operation requires that the frit glass is baked in ambient air or in a nitrogen atmosphere within a temperature range between 400 and 500xc2x0 C. for more than ten minutes.
Additionally, a display panel of the type under consideration is normally operated for image display by applying a high voltage between the electron source substrate 201 and the fluorescent film 204 arranged on the face plate 203, which are separated only by a short distance between 1 and 10 mm in order to avoid any undesired spread of electron beams. In other words, the intensity of the electric field between the electron source substrate 201 and the fluorescent film 204 will be as high as between 10xe2x88x926 and 10xe2x88x927V/m when a voltage of 10 kV is applied to the fluorescent film.
When the surface conduction electron-emitting devices are driven to operate under such an intense electric field, undesired phenomena such as abnormal electric charging and discharging can appear to destroy, in certain cases, some of the devices as residual molecules are ionized in the envelope 207 if the pressure in the envelope 207 is not held sufficiently low.
Particularly, the inside of the envelope 207 can become contaminated, at least temporarily, by the gaseous organic substance introduced into the envelope 207 for the activation process.
Therefore, the envelope 207 is preferably baked out at a temperature, for example, between 300 and 400xc2x0 C. for more than ten hours before it is hermetically sealed.
Thus, the components of the surface conduction electron-emitting devices need to show a sufficient resistance against heat in such a long heating operation conducted at temperatures as high as 400 or 500xc2x0 C. in some instances. However, such a dual requirement of thermal resistance and reduced power consumption for energization forming has hardly been met to date.
Under the above described circumstances, there has been a demand for a method of manufacturing a surface conduction electron-emitting device that can produce an electron-emitting region 5 within the electroconductive thin film 4 that is thermally highly resistive for the heating step with a low power consumption rate during the energization forming step.
In view of the above identified problems, it is therefore an object of the present invention to provide a method of manufacturing a surface conduction electron-emitting device that operates excellently for electron emission during a prolonged service life, a method of manufacturing an electron source comprising such surface conduction electron-emitting devices and a method of manufacturing an image-forming apparatus using such an electron source.
As a result of intensive research efforts, the inventors of the present invention achieved the present invention.
According to an aspect of the invention, there is provided a method of manufacturing an electron-emitting device having an electroconductive film including an electron-emitting region and a pair of device electrodes disposed opposite to each other and electrically connected to the electroconductive film, characterized in that it comprises steps of (a) producing a film of an organic metal compound or a complex thereof as a precursor of the material of the electroconductive film to link the device electrodes and (b) turning the film of the organic metal compound or the complex thereof, whichever appropriate, into an electroconductive film including an electron-emitting region by keeping the temperature of the film above the decomposition temperature of the organic metal compound or the complex thereof and applying a voltage to the film of the organic metal compound or the complex thereof by way of the device electrodes.
Alternatively, a method of manufacturing an electron-emitting device according to the invention is characterized in that it comprises steps of forming a first electroconductive film, forming a fissure in part of the first electroconductive film, subsequently producing a film of an organic metal compound or a complex thereof on the first electroconductive film and turning the film of the organic metal compound or the complex thereof, whichever appropriate, into a second electroconductive film including an electron-emitting region by keeping the temperature of the film above the decomposition temperature of the organic metal compound or the complex thereof and applying a voltage to the film of the organic metal compound or the complex thereof by way of the device electrodes. For the purpose of the invention, a pulse voltage may be applied to the device electrodes in the step of forming a fissure in the first electroconductive film.
In a broader scope, a method of manufacturing an electron-emitting device according to the invention is characterized in that it comprises steps of forming at least a pair of device electrodes, forming a film of an organic metal compound or a complex thereof and electrically energizing and baking the film of the organic metal compound or the complex thereof and subjecting the film to an activation process. In a preferred mode of carrying out the invention, the step of. electrically energizing and baking the film of organic metal compound or the complex thereof is conducted in an oxidizing atmosphere and the subsequent step of subjecting the film to an activation process is conducted in an organic substance containing atmosphere. In another preferred mode of carrying out the invention, the step of electrically energizing and baking the film of organic metal compound or the complex thereof is conducted in an inert gas containing atmosphere or in vacuum to incorporate the subsequent activation step in it. Alternatively, the step of electrically energizing and baking the film of organic metal compound or the complex thereof is conducted in an organic substance containing atmosphere to incorporate the subsequent activation step in it.
The present invention also relates to a method of manufacturing an electron source as well as to a method of manufacturing an image-forming apparatus comprising such an electron source.
In another aspect of the invention, there is provided a method of manufacturing an electron source comprising a plurality of electron-emitting devices arranged on a substrate, each having an electroconductive film including an electron-emitting region and a pair of device electrodes disposed opposite to each other and electrically connected to the electroconductive film, characterized in that the electron-emitting devices are prepared by means of any of the above described method of manufacturing an electron-emitting device.
In still another aspect of the invention, there is provided a method of manufacturing an image-forming apparatus comprising an electron source and an image-forming member for emitting rays of light to produce an image as it is irradiated with electron beams emitted from the electron source, said electron source and said image-forming member being contained in a vacuum container, characterized in that the electron source is prepared by the above described method of manufacturing an electron source.
In a further aspect of the invention, there is provided an electron-emitting device manufactured by a method of manufacturing an electron-emitting device according to the invention.
An electron-emitting device according to the invention comprises an electroconductive film including an electron-emitting region, a pair of device electrodes disposed opposite to each other and electrically connected to the electroconductive film and a coating film containing carbon as principal ingredient and covering the electron-emitting region, and is characterized in that the electric resistance of the electroconductive film does not irreversibly increase if its temperature is raised from room temperature to 500xc2x0 C. Preferably, the thermal aggregation temperature of the electroconductive film is not lower than 500xc2x0 C.
Alternatively, an electron-emitting device according to the invention comprises an electroconductive film including an electron-emitting region, a pair of device electrodes disposed opposite to each other and electrically connected to the electroconductive film and a coating film containing carbon as principal ingredient and covering the electron-emitting region, and is characterized in that the electric resistance of the film laminate does not irreversibly increase if its temperature is raised from room temperature to 500xc2x0 C. Preferably the thermal aggregation temperature of at least one of the layers of the film laminate except the lowermost layer is not lower than 500xc2x0 C.
In a still further aspect of the invention, there are provided an electron source and an image-forming apparatus.
An electron source according to the invention is characterized in that it comprises a plurality of electron-emitting devices according to the invention and wires for electrically connecting the devices arranged on a substrate.
An image-forming apparatus according to the invention is characterized in that it comprises an electron source according to the invention and an image-forming member for emitting rays of light to produce an image as it is irradiated with electron beams emitted from the electron source, said electron source and said image-forming member being contained in a vacuum container.
With a method of manufacturing an electron-emitting device according to the invention, there is realized an electron-emitting device that stably maintains its electron emitting performance for a long period of time.
With a method of manufacturing an electron source according to the invention, there is realized an electron source that also stably maintains its electron emitting performance for a long period of time.
With a method of manufacturing an image-forming apparatus according to the invention, there is realized an image-forming apparatus that stably maintains its image forming performance for a long period of time.